Gas-fired boilers or the like

ABSTRACT

A steam boiler or analogous heat exchanger is provided with a gas-fired burner comprising a plenum chamber from which a combustible gas-air mixture escapes through an inexpensive and readily replaceable burner member formed of foraminous ceramic material. The porosity and thermal conductivity of the burner member are such as to produce substantially flameless combustion toward the outer surface of the burner member, which causes that surface to incandesce and to radiate heat directly to waterfilled boiler elements facing the burner member.

United States Patent 3,211,133 10/1965 Valyi 122/33 3,315,646 4/1967Wilten, Jr. 122/235 3,418,979 12/1968 Reichmann 43 l/328X PrimaryExaminerKenneth W. Sprague 38 32 2s 78 A4. 21 a 21 :3 2 l8 3- laiaii ixia 23727 Patefiied Feb; 16, 1911 3,563,211

2 Sheets-Sheet 1 INVENTOR. LLOYD HORNBOSTEL JR.

P atented Feb. 16,1971 I 3,563,211

2 Sheets-Sheet 2 INVENTOR. LLOYD HORNBOSTEL. JR.

e e 1 1 t GAS-FIRED BOILERS OR THE LIKE BACKGROUND OF THE INVENTION- 1.Field of the lnverition The present invention relates to gas-fired steamboilers or analogousheat exchangers and more particularly to suchdevicesemploying surface combustion radiant burners.

2. Description of the Prior Art i i ln gasfired steam generating unitsat least four principal heat transfer mechanisms occur simultaneously;namely, nonluminous radiation from theproducts of combustion, luminousradiation fromburning particles of suspended solids carried by thecombustion gases, convection from the combustion gases and conductionbetween the boiler surfaces and hot particles deposited thereon duringcombustion. ln most types of boilers, radiation is the most significantof these mechanisms, particularly inthose portions of the boiler wherethe highest rate of steam generation takes place. Accordingly,

it has long been recognized that boiler efficiency can be improved byincreasing theamount of available heat energy which is transferred totheboiler surfaces byradiation; which is most commonly accomplished byemploying refractory firebrick furnace and boiler wall linings whichreradiate energy to the boiler surfaces when they become heated toincandescent temperatures. Due to the weight and relatively low strengthof such refractory firebrick.rriaterials, however, it is generallyimpracticable to employ such a construction to a meaningful extent inhigh output portable boilers, e.g. of the type employed in steamautomobiles.

If a combustible mixture of air and gas is forced through a porousrefractory material and ignited at the outer surface thereof while asufficient flow velocity is maintained to prevent combustionfromflashing back through such material, the outer surface ofthematerial adjacent the combustion is rapidly heated to an incandescenttemperature. Thereafter, the incandescent refractory material promotesthe combustion to the extent that the mixture burns with almost novisible flame but with high radiant energy output. Although suchso-called surface combustion'can be produced by means of a porous massof almost any type of refractory substance, a.

particularly desirable material for that purpose comprises a moldedcomposition of ceramic fibers bonded together to provide a relativelylight and self-supporting rigid structure of predetermined permeabilityand low thermal conductivity,

known means for achieving such combustion. Briefly, these objectives areaccomplished in accordance with the invention by providing a boiler,preferably of the water tube-type, with a gas-fired burner comprising aplenum chamber from which a combustible gas-air mixture escapes througha burner member formed of molded ceramic material of the general typedescribed above. When the combustible mixture is ignited at the outsidesurface of the burner member, the resulting previously describedincandescent surface combustion phenomena imparts a high proportion ofradiant energy to the boiler tubes or analogous water-filled elementsspaced from but facing the burner member. Due to the low thermalconductivity of the burner member material and the homogeneous porositythereof, the burner material adjacent the plenum chamber is kept 'at atemperature well bclowtheignition temperature of the combustible mixtureby the passage of unignited air and gas therethrough. Consequently,since the burner member is devoid of any sizeable individual passagewaysextending between its inner and outer surfaces, the possibility offlashback into the plenum chamber is positively avoided regardless ofthe flow velocity through the burner member. Additionally,

this relatively cool condition of the portion of the burner memberbeyond its outer combustion surface allows it to be sealed in gastightcooperation with the plenum chamber structure without compensating forlarge differences in thermal expansion, and without subjecting the jointsurfaces to high temperatures. in accordance with a preferned embodimentof the invention, this feature allows a gastigh't joint to be providedbetween the burner member and the mating surface of the plenum chamberstructure by means of a conventional resilient O-ring gasket.Preferably, the burner element is adapted to be removed and replaced ina simple and straightforward manner without recourse to any majordisassembly of the boiler or any significant interruption in itsoperation.

The configuration of the burner member is such as to present a maximumincandescent area thereof to the adjacent water-filled elements of theboiler. For example, the burner member may be in the form of arelatively flat disc confronting candescent burner surface may define acorresponding spiral Specific details of such materials and techniquesfor the production thereof are disclosed-in U.S. Pat. No. 3,l79,l56,which also illustrates and describesthe" use of that type. of materialas a burner element in a reflective-type gasfired radiant space heater.An example of a commercially available material particularly suitablefor such surface combustion applications in the product sold by theBabcock and Wilcox Co. of Augusta, Ga., under the trademark KAOWOOL.

At least years ago, experimental attempts were made to improve steamboiler performance by the employment of surface combustion firing.Briefly, these experiments involved filling the firetubes offiretube-type boilers with loosely packed lumps or particles ofarefractory material such as firebrick and effecting combustion of anair-gas mixture introduced into the refractory mass through central jetopenings in annular fireclay plugs partially closing the inlet ends ofthe tubes adjacent the tubesheet. While those experiments conclusivelydemonstrated improved heat transfer performance, and thereby potentialreduction in boiler flue lengths, this technique apparently enjoyedlittle or not practical application, presumably because of the obviousattendant difficulties and inconvenience involved in boiler cleaning,inspection and maintenance.

SUMMARY time rNvgNrroN g I The present invention contemplates improvingheat transfer rates in gas-fired steam boilers by the employment ofsurface combustion firing without involving any of the complications orinconveniences inherent in the above-described previously or helicalrecess partially surrounding the adjacent boiler tube to thereby furtherincrease the impingement of radiant energy on that tube. In variousembodiments of the invention a plurality of such burner elements ofeither similar or different configurations can be employed in a singleboiler, in which case each of such burner members can be replacedindividually whenever necessary.

Although the foregoing description refers to steam boilers, it will beapparent that the invention is equally applicable to water heaters orother analogous structures in which heat is imparted to a confined gasor liquid. Accordingly, it will be understood that the term boiler" asused herein is not confined strictly to conventional steam producingboilers but is intended also to encompass such related devices forheating various confined liquids or gases.

Various means for practicing the invention and other ad vantages andnovel features thereof will be apparent from the 1 following detaileddescription of illustrative preferred embodiments of the invention,reference being made to the accompanying drawings in which likereference numerals identify like elements.

BRIEF DESCRlPTlON OF THEv DRAWINGS In the drawings:

F IG. 1 is an exploded perspective view of a compact boiler according toa preferred embodiment of the present invention,

FIG. 3 isa cross-sectional elevational view ofa boiler in actapered edgesurfaces of those elements tightly against the cordance with analternate preferred embodiment of the inmating surfaces of the burnerseating cones. To further insure vention comprising a tubularcylindrical burner member surthe existence of a gastight seal betweenthe edges of the rounded bya helically disposed boiler water tube.burner elements and the respective burner seating cones, a 5heat-resistant resilient O-ring 38 is located in an annular DESCRIPTIONOF THE ILLUSTRATWE PREFERRED depression 39 in each of the two cones andis slightly flattened EMBODIMENT and squeezed into the adjacent burnerelement when the latter The illustrative embodiment of the inventiondepicted in is pressed into P e y the corresponding closure member- FIGS3 and 2 f the accompanying drawings is a very 1 Accordingly, it will beseen that the closure members pact gas-fired water tube boilerparticularly suitable for steam Cooperate wlthvthe burner l to dehhePlenum Chamautomobiles or other related applications. The boilerhousing, hers 41 which Combustible mixtures of and gas are identified bynumeral 12, is generally symmetrical above and mitted through mixingValves 42 removably attached to the below its horizontal center planeand comprises a central two elesure member? cylindrical wall member 13from which tapered burner seating the operatlhh of the holler, thecomhushble h cones 14 extend outwardly to peripheral flanges 15. Anannumlxture lhtmdfleed mto the Plenum chambers Permeates larchannel-shaped manifold member 16 surrounds the central threhgh theuhlformly Permeable h' elements portion of the boiler and is welded tothe outer surfaces of bustle" e defined y the lhhel' fflees e the burnercones 14 to define an annular exhaust chamber 17 provided elemehts'ahd yhher g when the holler first P m with outlet tubes 18, which can alsoserve to support the boiler 20 Operation, this combustible mixture isignited the unit. bustion chamber by a conventional spark plug or thelike pro- I h bl d b il a combustion h b li i 19 jecting into thecombustion chamber through a radial tube in fits snugly into thecylindrical wall member of the boiler housthe eXhauSt Chamber, asdepleted at numeral ing and includes radial holes aligned withcorresponding AS previously mentioned, the ignited mixture initiallyburns holes 22 in that n member This ring is made f a with a flameadjacent the inner surfaces of the burner elerefractory material, f bl fh same type f ld d ments. Under the influence of the heat thus producedadjacent ceramic fiber composition mentioned previously, which is alsothe inner burner Surfaces, those Surfaces S0011 become incanthe materialof which the hereinafter described burner eledescent. h r up n h r ingpr m ion of the comments are f d sh ll Slots 23 are l t d i h upperbustion process causes the air and gas mixture to burn near the andlower surfaces of the liner ring to receive and position the burnerSurfaces With little 0 Visible am ut with a high laterally projectingrods 24 of boiler tube support members 25 level of radiant energyemission. By virtue of the relatively nd 26, uniform porosity and lowthermal conductivity of the burner The three boiler tubes of theillustrative boiler are identified element material, however, thoseportions of the burner eleby numerals 27,28 and 29 and are all of flatspiral configuraments beyond the regions of surface combustion aremaintion. The primary boiler tubes 27 and 28 are supported tained at arelatively cool temperature, well below the ignition respectively bysupport members 25 and 26 above and below temperature of the combustiblegas mixture, by the cooling inthe planes defined by the upper and lowerfaces of the liner fluence of the unignited gases constantly permeatingring. The secondary boiler tube 29 is supported between thetherethrough. Consequently, this mode of burner construction primarytubes in generally parallel relation thereto. in FIG. 1, positivelyavoids the danger of combustion flashback through both ends of all threetubes are shown extending outwardly the burner elements and alsoeliminates the exposure of the through the boiler housing so that theycan be connected exburner sealing rings to potentially destructivetemperatures. ternally to one another, as well as to a feedwater pumpand Due to the conformation of the combustion surfaces of the controlvalve unit and to a stream manifold or the like. Howburner elements withthe configuration of the corresponding ever, it will be apparent thatthethree boiler tubes could be boiler tubes, it will be apparent thatradiant energy is impinged connected within the boiler housing in anydesired fashion so onto approximately half the total surface area ofthose tubes that only a single water inlet tube and single steam outlettube from the closely adjacent burner surfaces generally parallel wouldemerge through the housing. Preferably, the three tubes thereto.Additionally, the remaining surfaces of the tubes are are connected inseries to provide a so-called monotube-type of course also exposed toless concentrated but nevertheless boiler in which the secondary tubefunctions as a superheater very intense radiation, both directly fromthe burner elements or economizer. and also by reflection from therefractory liner ring. Ac-

Burner elements 31 are in the form of generally flat discs cordingly,very high rates of heat transfer are achieved, resultwith tapered edgesurfaces 32 which conform to the conical ing in a correspondingly highlevel of boiler efficiency as comconfiguration of the internal surfacesof the boiler seating pared to previously known boilers of comparablesimplicity cones 14. The smaller diameter faces of the burner elements 55 and compactness. By way of example, a simple small scale exareprovided with spiral grooves 33 conforming to the spiral perimentalboiler comprising a single flat spiral water tube form of the adjacentprimary boiler tubes. As previously heated by a flat gas-fired surfacecombustion burner accorddescribed, the burner elements are made of agas-permeable ing to the present invention was found to produce at least30 composition of bonded refractory fibers, Preferably, the percent morepower in terms of steam output compared to its burner elements areproduced in finished form bymolding corresponding power output whenheated with a similarly techniques, but it is also possible to machinesuch elements located conventional multiple orifice burner burning gasat from blocks or slabs of the above-identified KAOWOOL the same rateofconsumption. material or some other analogous material. To furtherimprove the thermal efficiency of the boiler illus- In the assembledboiler, burner elements 31 are supported trated in FIGS. 1 and 2, afeedwater tube, not shown, can surby the mating engagement of theirtapered edge surfaces with round manifold member 16, whereby some of theheat energy the tapered internal surfaces of the burner seating conesand of the exhaust gases within chamber 17 is devoted to preheatareoriented such that the primary boiler tubes are partially ing the boilerfeedwater. Similarly, if the boiler is tired by a received in thecorresponding burner element grooves 33 with vaporized liquid fuel suchas gasoline, a vaporizer or preheater the internal surfaces of thosegrooves in spaced confronting tube can also be provided within theannular exhaust relation to the adjacent external tube surfaces.Peripheral chamber. Appropriate insulative lagging obviously can also beflanges 34 of closuremembers 35 are attached to the corprovided aboutthe outer periphery of the boiler, but in auresponding flanges 15 bybolts 36 extending through gaskets l, tomotive applications it may bepreferable to surround the 37. Flanges 34 overlap the adjacent surfacesof the outer faces manifold member 16 with an air duct from which hotair can of the corresponding burner elements and thereby hold the 1 beobtained to supply heat to the interior of the automobile.

If it should be necessary to replace one of the burner elements of theboiler, this can be, accomplished simply by shutting off the flow ofcombustible gases to the boiler, disconnecting the mixing valve from thecorresponding closure member, and then unbolting and removing thatclosure member from the boiler housing. Therefore, if the boiler ismounted in such a manner as to provide suitable access to both of itsclosure members, such replacement of the burner elements can beaccomplished rapidly and conveniently without removing the boiler fromits mountings or disconnecting steam or water lines.

The monotube boiler shown in FlG. 2 to illustrate an alternateembodiment of the invention comprises a generally cylindrical housingmember 45 provided with an upper exhaust stack 46 and with a peripherallower flange 47. A tubular combustion chamber liner 48, similar to thepreviously described liner ring 19, fits into the boiler housing and isheld in place by disc member 49; the latter being provided withappropriate annular gaskets and sandwiched tightly between flange 47 andthe similar flange 51 of plenum chamber member 52 by bolts 53. Beyondbolts 53, holes 54 are provided through the two flanges and the discmember for the purpose of mounting the boiler in a stationary supportframe, not shown.

In accordance with this embodiment of the invention, burner element 55is formed of the same type of bonded fibrous ceramic material previouslydescribed and is in the form of a cylindrical tube closed at its upperend 56 and provided with a conical. lower flange 57. A metal supporttube 58, closed at its top end, extends upwardly with the upper face 59of its enlarged base portion 61 seated against the lower face 62 of theflanged lower end of the burner element. The portion of the support tubewithin the burner element is uniformly perforated with a pattern ofnarrow vertical slots 63, or the equivalent, whereas the larger baseportion of the support tube is provided with a plurality of largerradial holes 64.

When the burner element is installed in the boiler it is positioned incoaxial relation with the helical boiler tube 65 by the matingengagement of the conical burner element flange 57 with acorrespondingly tapered lip 66 defining a central opening in disc member49 and by the reception of the base portion of the support tube incentral opening 67 in the bottom wall 68 of plenum chamber member 52. Aremovable cover plate 69 is attached to the bottom wall of the plenumchamber with a gastight gasket by means of nuts 71 threaded onto studs72. When this cover plate is in place, it engages the lower end ofsupport tube 58 so that the latter forces the conical flange of theburner element into tight engagement with the mating tapered surface ofdisc member 49 and with O-ring 73, corresponding to the previouslymentioned O-ring 38. Accordingly, when a combustible gaseous mixture isintroduced into the plenum chamber member through a mixing valveconnected to inlet tube 74, it passes into the support tube throughradial holes 64 and then permeates outwardly through the perforatedupper portion of the support tube and through the adjacent cylindricalwall of the burner element. Upon being ignited in the combustion chamber75, the gaseous fuel mixture therefore burns at the surface of theburner element in the same manner described above, thereby impartingheat energy to the boiler tube both by direct and reflected radiation.

Although the boiler depicted in H0. 3 is somewhat less compact andefficient than the one illustrated in FIGS. 1 and 2, its very simpleconstruction may offset those comparative disadvantages in variousapplications; for example, in domestic steam or water heatingunits.Additionally, it will be apparent that maintenance of this unit is evenmore straightforward than in the case of the previously described unitinasmuch as only one element, namely cover plate 69, need be removed toprovide access to the removable burner element and support tube.

The invention has been described in detail with particular reference toillustrative preferredembodiments thereof, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention as described hereinabove and as defined in theappended claims.

I claim:

1. A boiler comprising:

a. a housing;

b. a water tube coil of generally flat spiral configuration supported insaid housing;

c. a disc-shaped burner element "made of porous refractory material ofsuch porosity and relatively low thermal conductivity that a combustiblegas mixture supplied to one surface of said burner element will permeatethrough said element to the opposite surface thereof and when ignitedadjacent said opposite surface will produce substantially flamelesssurface combustion of high radiant energy output at said oppositesurface;

d. means for supplying a combustible gas mixture to said one surface ofsaid burner element; and

e. support means supporting said burner element in said housing withsaid opposite surface thereof generally parallel to and in directconfronting relation to adjacent external surface areas of said watertube coil.

2. A boiler according to claim 1 in which said burner element includes aperipheral conical surface, said housing including means defining aplenum chamber and a conical support surface adapted to mate with theconical peripheral surface of said burner to support said burner elementin communication with said plenum chamber so that a combustible gasmixture within said plenum chamber is supplied to said one surface ofsaid burner element and permeates through said burner element to saidopposite surface thereof.

3. A boiler according to claim 2 including a burner seating memberengageable with said burner element adjacent said conical surfacethereof to seat said conical surface of said burner element firmly inmating contact with said conical support surface.

4. A boiler according to claim 3 including an annular O-ring sealadapted to be compressed between said mating conical surfaces of saidburner element and said support member.

5. A boiler according to claim 1 in which said opposite surface of saidburner element is provided with a generally semicylindrical grooveconforming to the configuration of said coil, said coil being partiallyreceived in said groove out of contact with said burner element.

6. A boiler comprising:

a. a boiler tube element including a pair of generally flat tubularcoils substantially parallel to one another,

b. a housing laterally surrounding said boiler tube element,

c. a pair of generally flat surface combustion burner elements supportedin said housing at opposite sides of said boiler tube element inparallel confronting relation to the adjacent ones of said tubularcoils,

d. plenum chamber means defining plenum chambers in communication withthe outwardly facing surfaces of said burner elements, and

e. means for introducing into said plenum chambers a combustible mixtureof gases which permeates through said burner elements and after beingignited adjacent the inwardly facing surfaces of said burner elementsproduces surface combustion at those surfaces.

7. A boiler comprising:

a. a housing including opposed conical housing sections taperingoutwardly from each end of a generally cylindrical central housingsection,

b. a boiler tube element including a pair of opposed generally flattubular coils substantially parallel to one another,

0. means supporting said boiler tube element within said central housingsection in substantially normal relation to the axis of said housing,

d. a pair of generally flat round surface combustion burner elementshaving tapered peripheral surfaces adapted to mate with said conicalsections of said housing to support said burner elements respectively inparallel confronting bustible mixture of gases which permeates throughsaid burner elements and after being ignited at the inwardly facingsurfaces of said burner elements produces surface combustion at thosesurfaces, and

g. exhaust means for conducting exhaust gases out of the boilercombustion chamber defined within said central housing section betweensaid burner elements and occupied by said boiler tube element.

1. A boiler comprising: a. a housing; b. a water tube coil of generallyflat spiral configuration supported in said housing; c. a disc-shapedburner element made of porous refractory material of such porosity andrelatively low thermal conductivity that a combustible gas mixturesupplied to one surface of said burner element will permeate throughsaid element to the opposite surface thereof and when ignited adjacentsaid opposite surface will produce substantially flameless surfacecombustion of high radiant energy output at said opposite surface; d.means for supplying a combustible gas mixture to said one surface ofsaid burner element; and e. support means supporting said burner elementin said housing with said opposite surface thereof generally parallel toand in direct confronting relation to adjacent external surface areas ofsaid water tube coil.
 2. A boiler according to claim 1 in which saidburner element includes a peripheral conical surface, said housingincluding means defining a plenum chamber and a conical support surfaceadapted to mate with the conical peripheral surface of said burner tosupport said burner element in communication with said plenum chamber sothat a combustible gas mixture within said plenum chamber is supplied tosaid one surface of said burner element and permeates through saidburner element to said opposite surface thereof.
 3. A boiler accordingto claim 2 including a burner seating member engageable with said burnerelement adjacent said conical surface thereof to seat said conicalsurface of said burner element firmly in mating contact with saidconical support surface.
 4. A boiler according to claim 3 including anannular O-ring seal adapted to be compressed between said mating conicalsurfaces of said burner element and said support member.
 5. A boileraccording to claim 1 in which said opposite surface of said burnerelement is provided with a generally semicylindrical groove conformingto the configuration of said coil, said coil being partially received insaid groove out of contact with said burner element.
 6. A boilercomprising: a. a boiler tube element including a pair of generally flattubular coils substantially parallel to one anotheR, b. a housinglaterally surrounding said boiler tube element, c. a pair of generallyflat surface combustion burner elements supported in said housing atopposite sides of said boiler tube element in parallel confrontingrelation to the adjacent ones of said tubular coils, d. plenum chambermeans defining plenum chambers in communication with the outwardlyfacing surfaces of said burner elements, and e. means for introducinginto said plenum chambers a combustible mixture of gases which permeatesthrough said burner elements and after being ignited adjacent theinwardly facing surfaces of said burner elements produces surfacecombustion at those surfaces.
 7. A boiler comprising: a. a housingincluding opposed conical housing sections tapering outwardly from eachend of a generally cylindrical central housing section, b. a boiler tubeelement including a pair of opposed generally flat tubular coilssubstantially parallel to one another, c. means supporting said boilertube element within said central housing section in substantially normalrelation to the axis of said housing, d. a pair of generally flat roundsurface combustion burner elements having tapered peripheral surfacesadapted to mate with said conical sections of said housing to supportsaid burner elements respectively in parallel confronting relation tothe corresponding ones of said tubular coils located between said burnerelements, e. cover members peripherally engageable with the outwardlyfacing surfaces of said burner elements to urge said burner elementsinto tight supported mating engagement with said corresponding conicalhousing sections and to define respective plenum chambers incommunication with the outwardly facing surfaces of said burnerelements, f. means for introducing into said plenum chambers acombustible mixture of gases which permeates through said burnerelements and after being ignited at the inwardly facing surfaces of saidburner elements produces surface combustion at those surfaces, and g.exhaust means for conducting exhaust gases out of the boiler combustionchamber defined within said central housing section between said burnerelements and occupied by said boiler tube element.